The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without payment of any royalties thereon or therefor.
The invention relates to magnetic bearings used in control systems and, more particularly, to a combination radial and thrust magnetic bearing that provides both radial and thrust axes control devices.
Bearings are used to rotatably support a shaft so it is maintained in the proper alignment required during operation, as well as to reduce fictional losses, noise, and wear. Typically, the shaft is centered within the bearings enclosure so that the shaft does not come into contact with the housing or the bearing enclosure itself as the shaft rotates. Magnetic bearings and non-magnetic or conventional mechanical bearings are two types of bearings that are typically used to rotatably support a shaft.
The types of conventional non-magnetic bearing include, for example, ball bearings, roller bearings and needle bearings. These bearings, however, have a number of disadvantages such as requiring the use of a lubricant to keep the bearings working properly, to reduce frictional losses and to dissipate heat energy. As such, bearings and bearing housing are designed to keep the lubricant from escaping, as well as to maintain the bearing in the proper alignment. Maintaining the proper lubrication becomes a problem as operational stress, rotational speeds and inherent temperatures increase.
The lubrication problems do not exist with magnetic bearings because they are the non-contact type bearings that effectively levitates or floats the rotating shaft/member by developed magnetic fields. Magnetic fields are developed by permanent magnets and/or electro-magnetically, by means of a closed-loop controller to provide appropriate currents to control coils such that appropriate magnetic fields are developed to provide stable positioning of the rotating shaft/member. Because magnetic bearings are non-contact bearings, there are no frictional losses resulting from contact, but rather there are rotational losses due to eddy-currents and hysteresis. These losses are typically much smaller than frictional losses. Also mechanical noise is typically reduced in comparison to conventional bearings because of the avoidance of mechanical erosion by magnetic bearings. Magnetic bearings used in control systems are known and some of which are described in U.S. Pat. Nos. 5,216,308 (""308); 5,514,924 (""924); 5,767,597 (""597); and 6,049,148 (""148). It is desired to further improve magnetic bearings. More particularly, it is desired that a single magnetic bearing unit of a compact design having improved performance be provided that has the capability to control a rotating shaft along the radial and thrust directions. Specifically, it is desired that a magnetic bearing be provided having independent magnetic flux paths for radial and thrust control coils such that the magnetic flux path does not flow through any bias magnets so that maximal coil efficiencies can be achieved. Moreover, it is desired to provide a magnetic bearing using laminated material for carrying magnetic fluxes used to develop both radial and thrust forces so as to minimize rotational losses. Furthermore, it is desired to provide a magnetic bearing of homopolar configuration in order to further minimize rotational losses. Moreover, it is desired to provide a magnetic bearing which has its radial x and y position sensors centrally co-located where the x and y activation force vectors act upon the shaft being levitated.
The invention is directed to a combination radial and thrust magnetic bearing that allow for both radial and thrust axes control of an associated shaft arranged therein.
The combination radial and thrust magnetic bearing provides magnetic fields used to control a shaft in both the radial and thrust axes. The combination radial and thrust magnetic bearing comprises a rotor and a stator. The rotor comprises a shaft, a first rotor pair having conical rotor elements separated from each other by a first spacer, and a second rotor pair having conical rotor elements separated from each other by a second spacer. The first rotor pair is separated from the second rotor pair by a sensor sleeve. A stator has first and second stator elements separated from each other by a magnet-sensor disk. The magnet-sensor disk has means to locate bias magnets and means to secure a plurality of position sensors. Each of the first and second stator elements, in one embodiment, comprises: (i) an inner flux ring; (ii) an outer flux ring; (iii) a thrust coil; (iv) a plurality of split poles with conically symmetric pole faces; and (v) a plurality of radial force coils one for each of the plurality of split poles and operatively connected thereto.
It is an object of the present invention to provide for a single homopolar magnetic bearing used for both radial and thrust axes control.
It is another object of the present invention to provide for radial and thrust force coils that can simultaneously and independently be used to provide magnetic forces in both the radial and thrust axes for control of an associated shaft.
It is a further object of the present invention to provide for position sensors and a control system that are utilized with a combination magnetic bearing for radial and thrust axes control of the associated shaft.
Further, it is an object of the present invention to provide for a magnetic bearing that can be equipped with separate thrust force coils and separate radial force coils to maintain independence of thrust and radial activation and control of the associated shaft.
It is another object of the present invention to provide for a magnetic bearing that minimizes both resistive and rotational losses by utilizing an efficient magnetic circuit design and a geometry which allows for practical use of laminated soft-magnetic material.
It is yet another object of this invention to provide for a magnetic bearing which has its radial x and y position sensors centrally co-located where the x and y actuation force vectors act upon the shaft being levitated.